This work presents the investigation of a solvent assisted bonding process developed for the fabrication of closed micro channels made from polymethylmethacrylate (PMMA). The effects of four processing parameters on the deformation and the bond strength of the micro channel have been investigated using the response surface methodology (RSM). High bond strengths (3.5 ± 0.8 MPa) at low deformations (1.6 ± 0.3 %) have been achieved at the center point of the design of experiment.
This work presents a new passive sensor concept for monitoring the deformation of orthopedic implants. The novel sensing principle of the WIPSS (wireless implantable passive strain sensor) is based on a hydro-mechanical amplification effect. The WIPSS is entirely made from biocompatible PMMA and consists of a microchannel attached to a reservoir, which is filled with an incompressible fluid. As the reservoir is exposed to strain, its volume changes and consequently the fill level inside the microchannel varies. The wireless detection of the microchannel's strain-dependent fill level is based on ultrasound. The WIPSS' sensing principle is proved by finite-element simulations and the reservoir's design is optimized toward maximum volume change, in order to achieve high sensitivity. A fabrication process for WIPSS sensor devices entirely made from PMMA is presented. The obtained measurement results confirmed the sensor's functionality and showed very good agreement with the obtained results of the conducted FE simulations regarding the sensor's sensitivity. A strain resolution of 1.7 ± 0.2 × 10 −5 was achieved. Further, the determination of the cross-sensitivity to temperature and strains applied out of the sensing direction is presented. The response to dynamic inputs (0.1-5 Hz) has been measured and showed decreasing sensor output with increasing frequency. Test structures of the sensor device allow the application of a signal bandwidth up to 1 Hz. Therefore, the proposed sensor concept of the WIPSS presents a promising new sensor system for static in vivo strain monitoring of orthopedic implants. In combination with the developed ultrasound-based read-out method, this new sensor system offers the potential of wireless sensor read-out with medical ultrasound scanners, which are commercially available.
In the present work, the applicability of the copper free silver based alloys Ag-15Mn and Ag-5Pd as filler metals for shielding gas brazing of the martensitic stainless steel X3CrNiMo13-4 was investigated. The joints were examined with respect to their microstructure, their corrosion behaviour in aequous NaCl solution as well as -in the case of the specimens brazed with AgPd5their mechanical performance under tensile and torsion loading. Specimens brazed with Ag-15Mn showed pronounced oxidation in the Ar/H 2 shielding gas atmosphere as well as a low corrosion resistance in 0?5M NaCl solution. The filler metal Ag-5Pd showed very good brazing results. With this filler metal, defect free and corrosion resistant joints with an ultimate tensile strength of 800 MPa and a low cycle fatigue strength of 490 MPa could be produced.
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